The present invention relates to flight path information systems and, more particularly, to flight path information assemblies, computer program products and methods for displaying flight path deviation information based on navigation system performance.
In modem commercial aircraft, a flight crew makes flight plan entries and modifications through a Flight Management Systemxe2x80x94Control Display Unit (FMS-CDU). The FMS-CDU is an electronic module containing a keyboard on its lower face half and an electronic display on its upper face half. By keying entries into the keyboard, the flight crew can build or modify a route into the Flight Management Computer by typing in a series of waypoints which are then displayed, in text form, on the upper half of the FMS-CDU display.
An additionally provided display is a navigation (map) display. In contrast to the text display of the FMS-CDU, the navigation display graphically depicts the selected waypoints along a desired route. Thus, as the flight crew types entries into the FMS-CDU, these are then displayed graphically on the navigation display.
Current FMC""s provide for construction of a variety of flight plans, consisting of dot-to-dot leg segments and procedural maneuvers. In addition, conventional FMC""s provide an autopilot mode where the aircraft automatically flies according to a predefined flight plan by providing lateral navigation (LNAV) and vertical navigation (VNAV) guidance so that the route can be flown. Most commercial airliners can be flown on a constant heading with the autopilot engaged. This allows interception and tracking of a course outbound from a geographical waypoint. However, due to the effect of wind on the flight plan and other factors, the actual flight path flown by the aircraft often differs from the predefined flight plan, thus requiring constant adjustment to the airplane heading to maintain the desired course.
In order to facilitate adjustment of the airplane heading to maintain the desired course, many conventional FMC""s are also capable of determining the position of the aircraft from navigation systems, such as GPS (Global Positioning System), ILS (Instrument Landing System), IRS (Inertial Reference System), VOR (VHF Omni-directional radio Range) and DME (Distance Measuring Equipment). While these sources can provide adequate positioning information, they each have individual drawbacks. For example, while systems such as GPS systems, which acquire positioning information from satellites, can provide positioning information to an aircraft virtually anywhere, the availability of such satellite-based systems can be limited due to factors such as satellite geometry. And while ILS-type systems provide very accurate positioning information, these type systems are ground-based systems and are generally limited to landing procedures at major airports.
Due to the variances in the accuracy of many navigation systems, the United States and international aviation communities have adopted the Required Navigation Performance (RNP) process for defining aircraft performance when operating in enroute, approach and landing phases of flight. RNP is a probabilistic approach to evaluating an aircraft""s deviation from its intended course, and has been defined by the International Civil Aviation Organization (ICAO) as xe2x80x9ca statement of the navigation performance accuracy necessary for operation within a defined airspace.xe2x80x9d Currently, several definitions of RNP standards exist, including Boeing RNP, Airbus RNP, RNP-10 and BRNAV/RNP-5. In this regard, according to the Boeing RNP, the navigation performance accuracy can be quantified by a distance in nautical miles, and a probability level of 95% laterally and 99.7% vertically. For example, an aircraft is qualified to operate in an RNP 1 lateral, RNP 250 vertical airspace if it can demonstrate that the capability and performance of the aircraft""s navigation system will result in the aircraft being within 1 nmi (nautical miles) lateral of the indicated position on the navigation system at least 95% of the flying time, and within 250 feet vertical of the indicated position at least 99.7% of the flying time.
Expanding upon the lateral navigation accuracy performance standard of 95%, the Boeing RNP defines a lateral integrity containment limit of twice the size of the RNP, centered on the aircraft""s predefined path. The integrity containment limit further specifies that the navigation system must ensure the aircraft remains within the integrity containment boundary 99.999% of the flying time.
Currently, to determine whether an aircraft is within the RNP or integrity containment limit, the FMC""s calculate a real-time estimate of the navigation system accuracy, commonly referred to as the actual navigation performance (ANP). The ANP is typically calculated by the FMC based upon fault free performance and integrity statistics provided by the GPS receivers or the aircraft""s geometry relative to ground based navigation aids, and assumptions on the navigation aid survey location error and performance characteristics. The ANP and RNP are then typically displayed on the FMS-CDU in numeric form along with a large amount of other numerics and text information relating to the intended flight path of the airplane. In order to determine whether the ANP is within the RNP, the display system provides for an xe2x80x9cUNABLE RNPxe2x80x9d alert when ANP exceeds RNP. This alert does not directly account for RNP changes due to the airplane deviating from the defined path. To account for this, the pilot or other crew member must look at the lateral path deviation displayed on the aircraft Navigation Display and the altitude displayed on the aircraft Primary Flight Display and attempt to determine if the deviation is acceptable for the selected RNP. This display and comparison method of determining whether the ANP is within the RNP requires an unnecessary amount of time, can be very distracting for the pilot and/or air crew member, and is only marginally adequate for low RNP values.
In light of the foregoing background, the present invention provides an assembly, computer program product and method for displaying navigation performance based flight path deviation information. The assembly, computer program product and method of the present invention provide pilots and/or air crew members with a clear, concise display of the dynamic relationship between ANP and RNP, intersecting flight paths and current actual flight path deviation from a predefined flight path. Also, whereas ILS guidance systems are generally limited to landing procedures at major airports, the assembly, computer program product and method of the present invention provide a deviation display operable for a wider range of airport procedures, including departures, arrivals and approach transitions.
According to one embodiment, a navigation performance based flight path deviation display assembly includes a display and a display processor capable of generating an image upon the display. The image includes at least one flight path scale comprising a reference point bounded by end markers extending in at least one of a lateral and vertical direction, such as the end markers extending equidistant laterally and/or vertically from the reference point on a respective flight path scale. The reference point relates to an actual flight path, and the end markers represent a required navigation performance (RNP). The display also includes at least one moveable deviation pointer disposed on the flight path scales, where the deviation pointer moves between the end markers based upon a deviation of the actual flight path of the aircraft relative to a predefined flight path.
Additionally, the image includes a representation of at least one extendable navigation error disposed on the flight path scale, which defines at least one navigation performance suspect region. The representation extends from at least one of the end markers toward the reference point based upon the actual navigation performance (ANP) and the RNP for the aircraft, where the ANP and RNP are based upon a flight phase of the aircraft. In another embodiment, the representation is capable of identifying the at least one deviation pointer on the representation.
In another embodiment, a flight path intersection display assembly comprises a display and a display processor capable of generating an image upon the display comprising the flight path scales and the deviation pointers. In addition, the image includes at least one moveable intersecting flight path pointer disposed on the flight path scales. The intersecting flight path pointers move in the area between the end markers based upon a distance of the intersecting flight path from the actual flight path.
In operation, the method for providing navigation performance based flight path deviation information begins by providing the flight path scales. Then, a deviation of the actual flight path of the aircraft relative to a predefined flight path is determined, and the moveable deviation pointers are thereafter displayed on the flight path scales based upon the deviation and the reference point. Next, an actual navigation performance (ANP) and the RNP are determined based upon a flight phase of the aircraft, and a representation of at least one extendable navigation error is thereafter displayed on the flight path scales based upon the ANP and RNP. In a further embodiment, deviation pointers on the representation are identified. In embodiments including the intersecting flight path pointers, after displaying the representation, at least one intersecting flight path is identified, and the moveable intersecting flight path pointers are thereafter displayed on the flight path scales based upon a distance of the intersecting flight path from the actual flight path.
The various embodiments of present invention therefore provide pilots and/or air crew members with a clear, concise display of the ANP as it relates to the RNP, intersecting flight paths and current actual flight path deviation from a predefined flight path. The non-distracting and intuitive display of the present invention also allows pilots and/or air crew members to readily determine in a timely manner whether the current navigation performance of the aircraft is within the required navigation performance.